We wish to explore the possibility that postnatal maturation of the central nervous system may play a major role in cognitive development. Our strategy is to study, in normal children, the ability to perform tasks which differentiate various subgroups of adults with lesions in different parts of the brain. In particular, we will assess some of the visuo-spatial capacities which seem to depend, in adults, on the integrity of the right cerebral hemisphere. One such task, we have found, is recognition of faces, which shows a sharp developmental discontinuity at age 10. Additional experiments are proposed to characterize further the nature of the deficit in face perception in young children. We will attempt to establish whether maturation of a specific processor for faces is implicated. Alternatively, we will explore the possibility that the discontinuity in performance on face identification tasks reflects development of more general abilities for perceptual classification. These capacities might also depend upon maturation of the right hemisphere. Perceptual classification has been described as mediated by prototypes, or canonical representations of objects, plus specifications of permissible deviations from the prototype. In adults, tolerance for deviations is selectively impaired by certain right hemisphere lesion. We intend to investigate the course of acquisition of this form of mediation (by prototype or schema, and deviations) with special attention to possible discontinuities at age 10.